Conidiomatal Morphogenesis and Pleomorphic Conidiogenesis in Scleroconidioma sphagnicola

Morphogenesis of microsclerotia and conidiomata, and conidiogenesis in Scleroconidioma sphagnicola were studied primarily by transmission and scanning electron microscopy. Microsclerotia were initiated as bulges from hyphae that later swelled and became multicellular. They increased in size by forming protrusions that subsequently were delimited by multilayered, simple septa. The structure of septa indicated an ascomycetous affinity. Cells of mature microsclerotia contained large lipid bodies and poorly defined organelles. In culture, microsclerotia often became conidiomata by conversion of the surface cell layer to conidiogenous cells. These conidiogenous cells were either percurrently proliferating or were phialides with a collarette and periclinal wall thickening. Conidia were also produced from vegetative hyphae. Conidiogenous cells arising from juvenile, hyaline hyphae proliferated percurrently or occasionally sympodially with the production of successive conidia. As the colony aged and hyphae became darkly pigmented, variously shaped, solitary hologenous conidia became more dominant. Secondary conidiation from these conidia was frequent. Relative juvenility of the cell wall at the conidiogenous locus and the age of the colony appear to be important factors in determining the mode of conidium development in S. sphagnicola.